I wouldn't recommend running 200 anyway as I suspect it would ride like there was no front suspension. At 60 P/SI it's impossible to compress the fork...well at least with my 260lbs pushing straight down on it anyway....no give at all, that i could detect.
Roughly knowing the upper limits is for determining how much of a safety ceiling is available above more realistic pressures before you need to be concerned about having a catastrophic failure.
I'd expect with no spring in, the upper comfortable ride/ good handling limit would be around 60-70 P/SI.
Which for comparison is 50-40 P/SI below the pressure in my racing bicycle's ultra thin skinned super narrow tires. (110 P/SI)
80 is dead on for my '71 Schwinn 10 speed's tires which are also very thin skinned. But I think the surface area of the contact patch for it is very telling. For the '71 the contact patch of both tires (occasionally only one tire bearing the full load
) supporting about 290lbs of rider and bike is about the size of a quarter per tire, and yields a very bone shaking ride on anything but the smoothest of pavement. You literally feel every pebble and crack.
A quick look at the Vol's builder's plate shows GVW to be 1025lbs, GAWF 355lbs, GAWR 670lbs.
To put that into perspective our fork tubes have more than 100% greater surface area ( 982mm\2 VS 2267.08mm\2
) at the ends supporting a recommended maximum of 55lbs more weight. (wonder what the wheels and tires weigh, I also wonder if those weights are at the axle including wheel and tire weight or not. If they include wheel and tire I suspect there is close to 30lbs less weight on the fork at maximum allowable load, not including the weight of the sliders which are also not part of the weight carried by the springs. and therefore would result in roughly only 320lbs being borne by the upper suspension).
So in short anything over 80 P/SI is very likely serious overkill, and very likely going to negatively affect comfort and handling. 80 P/SI yields 283lbs of force required before the fork even attempts to begin to compress. Of course as it compresses air pressure increases requiring increasingly more force required to compress further.
Using the realistic estimate of 200 as the likely to fail limit leaves a ceiling of 120P/SI to account for a good safety margin. To run any pressure vessel at it's working limit is foolish at best (despite the failure rating being typically 150%-200% of the working pressure).....just like running an engine at it's mechanical limits. Sooner rather than later it will fail.